JPH06196760A - Superconductive lamination thin film - Google Patents

Abstract

PURPOSE:To provide a superconductive lamination thin film applicable to a microwave element such as a circulator by compounding an oxide superconductor and a magnetic material. CONSTITUTION:This superconductive lamination thin film has the structure in which an oxide superconductor thin film 2 such as Y-Ba-Cu-O and Ti-Ba-Ca- Cu-O is made to perform heteroepitaxial growth on a single crystal substrate 1 of a rare earth iron garnet. Further, SrTiO3, LaAlO3 and MgO are formed between the oxide superconductor thin film 2 and the rare earth iron garnet substrate 1 as a buffer layer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an oxide superconducting laminated thin film having a high critical temperature (T _C ).

[0002]

Since the discovery of the Related Art oxide with a high T _C superconductor, basic research and applied to electronic devices such studies for superconducting Mechanism have been actively bring its high T _C. Among various oxide superconducting materials containing copper, Y-based superconductors and Tl-based superconductor oxide superconductors can use inexpensive liquid nitrogen having a boiling point of 77K as a refrigerant.
It also has the advantage that simple equipment can be used for keeping the temperature low. Therefore, compared with the conventional superconducting material with low T _C , which used expensive liquid helium, it is necessary to manufacture superconducting magnets, Josephson junctions, SQUIDs, etc. with high-temperature oxide superconductors. Will make a major contribution to the industry. As a technology for utilizing the oxide superconductor, in addition to the digital device such as the Josephson junction used in the Nb-based superconducting material, the surface resistance peculiar to the superconducting material is low, and the frequency dispersion is small. Utilizing this, application to microwave devices is also possible. Specifically, it can be applied to resonators, filters, delay lines, etc. using oxide superconducting materials. When such an element is realized by using an oxide superconductor, a low-loss high-performance microwave passive that cannot be realized by using a conventional normal conductive material due to the low surface resistance of the oxide superconductor. The device can be manufactured. Further, the microwave integrated circuit can be downsized by combining such a filter with other elements. A circulator is an example of such an element for forming a composite. The circulator is widely used in microwave integrated circuits as a non-reciprocal circuit, but there is a problem that the characteristics of the conventional planar circulator are limited by the loss of the strip conductor.
Therefore, if it becomes possible to use an oxide superconductor for this strip conductor, it becomes possible to dramatically improve the characteristics of the circulator.

[0003]

However, in order to realize such a circulator, it is necessary to combine an oxide superconductor with a magnetic substance. However,
In the prior art, the oxide superconductor is generally formed on a single crystal substrate of a non-magnetic material such as SrTiO ₃ , LaAlO ₃ or the like having a perovskite structure, and a magnetic material. No compounding was done. An object of the present invention is to provide a superconducting laminated thin film which can be applied to a circulator or the like when producing an oxide superconductor thin film containing copper.

[0004]

According to the present invention, a garnet type magnetic oxide having a general formula of R ₃ Fe ₅ O ₁₂ (R is Y, S
One or a combination of two or more selected from m, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu. ) A superconducting laminated thin film having a structure in which an oxide superconductor containing copper is formed on a rare earth iron garnet represented by), and a garnet-type magnetic oxide represented by the above general formula SrTiO on rare earth iron garnet
A superconducting laminated thin film having a structure in which ₃ , LaAlO ₃ or MgO is formed as a buffer layer, and an oxide superconductor containing copper is formed on the buffer layer.

[0005]

In the present invention, the Y-Ba-Cu-O system and Tl are used.
The reason why an oxide superconductor containing copper such as —Ba—Ca—Cu—O system was grown on a substrate of a magnetic material is that the oxide superconductor and the magnetic material are different from each other in consideration of application to a circulator or the like. This is because compounding is required. Further, the oxide is used as the magnetic material because the superconducting material is an oxide, whereas the use of the metal-based magnetic material causes the magnetic material to be oxidized during the thin film production to deteriorate the magnetic characteristics. This is because the oxide magnetic material does not cause such a problem in the compounding with the oxide superconductor and has excellent compatibility with both.
Further, the rare earth iron garnet represented by R ₃ Fe ₅ O ₁₂ was used as the oxide magnetic material because a single crystal substrate of this material can be easily obtained. This is because it is possible to synthesize a single crystal thin film.

Next, when SrTiO ₃ or LaAlO _{3 having} a perovskite structure and MgO having a NaCl type structure are used for the buffer layer, oxide superconductivity in which these materials have a lattice constant containing copper more than that of the rare earth iron garnet. Since it is close to the lattice constant of the body, the misfit between the lattices of the two is relaxed, which improves the epitaxial property of the oxide superconductor and reduces the crystal imperfections. The superconducting property of is further improved.

[0007]

EXAMPLES Next, examples of the present invention will be described. In this embodiment, Y-Ba-Cu-O system and Tl-Ba are used.
-Ca-Cu-O-based oxide superconducting material and SrTiO
_A multi-source excimer laser deposition apparatus was used to produce a thin film of a buffer layer of ₃ , LaAlO ₃ or MgO. In this equipment, the target energy is instantaneously blown by the high energy density of the excimer laser, so the composition of the thin film does not deviate from the composition of the target, and it is possible to produce a thin film with the desired performance with extremely good reproducibility. There are features. In the thin film production, Y-Ba-Cu-O system or Tl-B is used in the deposition chamber.
a-Ca-Cu-O based target, as well as SrTiO _3, LaAlO _3, or MgO target for the buffer layer formation provided was carried out by heating the evaporation of each of the target by the laser.

FIG. 1 is a diagram showing the structure of a superconducting laminated thin film according to an embodiment of the present invention. Rare earth iron garnet R ₃ Fe ₅ O ₁₂ (R is Y, Sm, Eu, Gd, Dy,
A single crystal of one of Ho, Er, Tm, Yb, and Lu, or a combination of a plurality of these) was used.
In particular, in this example, Y ₃ Fe ₅ O _{12 in} which R is Y was mainly used for the study. In the present embodiment, the thin film 2 was selected from YBa ₂ Cu ₃ O _x as the Y-based superconductor and Tl ₂ Ba ₂ CaCu ₂ O _x as the Tl-based superconductor. 2 is a diagram showing the structure of another embodiment of the present invention, in which the buffer layer 3 is provided between the rare earth iron garnet substrate 1 and the oxide superconductor thin film 2.
Are formed. As the buffer layer 3, SrTi
O ₃ , LaAlO ₃ , and MgO were used with a thickness of about 100 Å, and the thickness of this buffer layer was 5
If it is 0 angstrom or more, it is okay.

First, examples of the Y-based superconductor will be described in detail. In this case, the target is YBa
_A sintering target close to the stoichiometric composition of ₂ Cu ₃ O _x was used. The Y ₃ Fe ₅ O ₁₂ single crystal garnet substrate was placed on the substrate holder and heated to a substrate temperature of about 600 to 700 ° C. The size of the substrate is 30mm square and the thickness is 0.5mm.
And Before film formation, after performing pre-sputtering for about 30 minutes with the substrate shutter closed, the shutter was opened and a thin film was deposited on the substrate. By setting the oxygen partial pressure in the deposition chamber during film formation to 200 mTorr and the frequency of the excimer laser to 3 Hz, the Y-based superconductor thin film could be formed at a deposition rate of about 2.5 angstrom / sec. . Finally, the thickness of the Y-based superconductor thin film is 5
000 angstrom.

When the composition of the thin film thus produced was examined by an electron probe microanalyzer (EPMA), it was found to be YBa ₂ Cu ₃ O _X , which is almost close to the stoichiometric composition, and there is almost no deviation from the target composition. I knew it wasn't. Further, when the structure of the thin film was examined by the X-ray diffraction method, it was found to be the structure of a Y-based superconductor with c-axis orientation, and no heterogeneous phase was observed. Further, since the c-axis lattice constant is 11.69 angstroms, which is close to the bulk value, it was found that a superconducting structure was obtained without heat treatment. Furthermore, when this thin film was analyzed by a secondary ion mass spectrometer (SIMS), the interface between the Y-based superconductor thin film and the Y ₃ Fe ₅ O ₁₂ substrate was steep, and no mutual reaction occurred. Scanning electron microscope (SE
When observed under M), it was confirmed that the surface of the thin film was flat and no clear crystal grains were observed, and the film was almost a single crystal thin film. When this thin film was evaluated by electric resistance measurement, it was T _c ˜89 K as shown in Table 1, and 7
It was found that the critical current density J _c at 7 K was 2 × 10 ⁶ A / cm ^2, which was a very excellent superconducting property. Also, Nb
An evaluation of the surface resistance (Rs) using a cavity showed that it was 300 μΩ at 77 K and 10 GHz, which was sufficiently smaller than that of the normal conductor Cu and was sufficiently applicable to a microwave element with low loss. . Further, even if a rare earth iron garnet other than Y ₃ Fe ₅ O ₁₂ was used as the substrate, almost the same superconducting characteristics could be obtained.

Next, before depositing the Y-based superconductor, Y ₃
SrTiO ₃ , LaAlO ₃ or MgO was formed as a buffer layer on the Fe ₅ O ₁₂ single crystal substrate. Specifically, one of these is selected as a target, the substrate temperature is set to 400 to 500 ° C., which is lower than the temperature for producing the Y-based superconductor thin film, and the other conditions are the above-mentioned Y-based superconductivity. 10 under the same conditions as for body thin film production
A film of about 0 angstrom is formed. After the film formation of the buffer layer was completed, the target was replaced with the target of the above Y-based superconductor, and a Y-based superconductor thin film of about 5000 angstrom was formed on the buffer layer at a substrate temperature of 600 to 700 ° C. .

When the structure of the laminated thin film thus obtained is observed by SIMS, both the interface between the buffer layer and the garnet substrate and the interface between the Y-based superconductor thin film and the buffer layer are sharp and no reaction or the like has occurred. Was confirmed. In addition, evaluation by X-ray diffractometry, SEM, etc. revealed that the crystallinity of the thin film was further improved by employing the buffer layer. Further, as shown in Table 1, it can be seen that the superconducting property is also improved by using the buffer layer. Furthermore, even when a buffer layer was provided, almost the same superconducting characteristics could be obtained even if a rare earth iron garnet other than Y ₃ Fe ₅ O ₁₂ was used as the substrate.

In the case of the Tl-based superconductor, unlike the case of the Y-based superconductor, it becomes difficult to produce a superconductor thin film without heat treatment. This is because in the case of Tl system, since the vapor pressure of Tl is high, it becomes difficult to form a thin film having a stoichiometric composition on a high temperature substrate by the excimer laser deposition method. Therefore, in this example, a Tl-based superconductor thin film was produced by performing heat treatment after film formation. The process is briefly described below. First, Tl ₂ Ba ₂ C was deposited on a Y ₃ Fe ₅ O ₁₂ substrate kept at room temperature.
An aCu ₂ O _x target is heated and vapor-deposited by an excimer laser to form a thin film of about 5000 angstrom. Also in this case, the composition of the thin film was almost the same as the target composition. At this time, the structure of the thin film is amorphous, and electrically exhibits insulator-like characteristics. This thin film was mixed with bulk Tl ₂ Ba ₂ CaCu ₂ O _x at 1 atm of oxygen for 8 hours.
It heat-processed at 00-850 degreeC for 1 hour. Bulk Tl ₂ B
a ₂ CaCu ₂ O _X is used to adjust the vapor pressure of Tl during the heat treatment. By this heat treatment, the thin film is changed to a c-axis oriented Tl-based superconductor thin film. SrTiO ₃ ,
When using a buffer layer of LaAlO ₃ or MgO, first, Y ₃ Fe ₅ is used at a substrate temperature of 400 to 500 ° C.
These thin films were formed on an O ₁₂ substrate, and an amorphous Tl ₂ Ba ₂ CaCu ₂ film was formed thereon at room temperature in the same manner as in the above case.
O _X film was formed, to prepare a superconducting thin film of the by then for 1 hour heat treatment at 800 to 850 ° C..

Regarding the thin film thus obtained, S
When analyzed by IMS, no mutual diffusion was observed between the Tl-based thin film and the substrate or buffer layer, confirming that a good quality thin film was obtained. In addition, X-ray diffraction method and SEM
It was also found from the evaluation by 1. that a Tl-based superconducting thin film having excellent crystallinity and a relatively good surface condition was obtained. Regarding the superconducting properties of these thin films, as shown in Table 1, T _c exceeding 100K and 1 at 77K were obtained.
_{Jc and the} like exceeding 0 ⁶ A / cm ² were obtained, which proved to be extremely excellent. Furthermore, 77K, 10GHz
The surface resistance in Example 2 also showed a comparatively low value of about 250 μΩ, and it was found that it can be sufficiently applied to a microwave element as in the case of the Y-based superconductor. Further, even if a rare earth iron garnet other than Y ₃ Fe ₅ O ₁₂ was used as the substrate, almost the same superconducting characteristics could be obtained. Next, Table 1 shows the details of the superconducting thin films produced in the above examples.

[0015]

[Table 1]

[0016]

As described above, the present invention provides a high-quality oxide superconducting laminated thin film on an oxide magnetic substrate, and is useful for applying an oxide superconductor to a microwave device. And the effect is great.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a laminated structure of a superconducting laminated thin film according to the present invention.

FIG. 2 is a diagram showing another example of the laminated structure of the superconducting laminated thin film according to the present invention.

[Explanation of symbols]

 1 Rare earth iron garnet 2 Oxide superconductor thin film 3 Buffer layer

Claims (2)

[Claims] 1. A garnet type magnetic oxide having a general formula of R ₃ Fe ₅ O ₁₂ (R is Y, Sm, Eu, Gd, Dy, H).
One or a combination of two or more selected from o, Er, Tm, Yb and Lu. ) A superconducting laminated thin film having a structure in which an oxide superconductor containing copper is formed on a rare earth iron garnet represented by. 2. A garnet type magnetic oxide having a general formula of R ₃ Fe ₅ O ₁₂ (R is Y, Sm, Eu, Gd, Dy, H).
One or a combination of two or more selected from o, Er, Tm, Yb and Lu. ) SrTiO ₃ , LaAlO ₃ or MgO on the rare earth iron garnet
Is formed as a buffer layer, and a superconducting laminated thin film having a structure in which an oxide superconductor containing copper is formed on the buffer layer.